JP2007099526A - Glass preform lot, its production method, and method for production of optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass preform lot or molded body (base material) lot in which the volume variation between respective preforms or molded bodies is highly controlled. <P>SOLUTION: The glass preform lot or preform base material lot is composed of a spherical preform or preform base material comprising glass whose SiO<SB>2</SB>content is regulated within the range of 0 to 20 mass% and in which an average mass is ≤200 mg and the ratio of mass tolerance to the mass is within ±0.3%. The method for production of the glass preform lot or glass molded body lot comprising the plurality of glass preforms or molded bodies comprises dropping the glass drip having a prescribed mass from the outflow port of an outflow nozzle, performing the precision press-molding of the obtained glass drop, and repeating the above process. An optical element is produced by heating the glass preform taken out from its lot and performing the precision press molding using the mold for press molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glass preform lot composed of a plurality of glass preforms used when a glass optical element is manufactured by precision press molding, a production method thereof, and a method of manufacturing an optical element.

  A precision press molding method is known as a technique for manufacturing glass optical elements such as aspherical lenses with high accuracy. This method is also called a mold optics molding method, which uses a press mold having a precisely machined molding surface to press-mold a heated glass preform to mold the shape of the entire optical element. The optical function surface is formed by precisely transferring the surface to glass. Such a method is disclosed in Patent Document 1, for example.

Further, the glass preform used for manufacturing the optical element is, for example, disclosed in Patent Document 2, outflowing molten glass, separating a molten glass lump of a desired mass, this glass lump is It can be produced by a method of forming into a preform in the process of cooling.
JP-A-10-316448 JP 2002-121032 A

  In recent years, there has been an increasing demand for small devices incorporating an imaging device, such as mobile phones with cameras. An image pickup optical system incorporated in such an image pickup apparatus is preferably composed of ultra-small lenses, and is preferably provided with a positioning reference surface for precisely positioning and fixing each lens. For example, as a positioning reference surface for precisely determining the distance between lenses, a flat surface provided on the outer periphery of the lens surface is used, and as a positioning reference surface for aligning the optical axes of the lenses, the lens side surface is used. Can do. Precision press molding not only allows precise formation of optical functional surfaces, but also allows precise formation of the positional relationship and angle between surfaces formed by transferring the molding surface including the optical functional surface. If the mold forming surface is transferred and formed, the optical function surface and the positioning reference surface can be formed in a lump.

  As described above, if the characteristics of precision press molding are utilized, an ultra-small optical element can be efficiently manufactured. On the other hand, if the volume of the preform is not precisely controlled, the following problems occur.

  First, when the volume of the preform is larger than the volume of the space formed in a state where the press mold is closed, between the mold members constituting the press mold, for example, between the upper mold and the barrel mold or the lower mold It protrudes between the body and the body mold and becomes a molding burr, which impairs the slidability of the mold and causes production stoppage or damage to the press mold.

  On the other hand, when the volume of the preform is smaller than the volume of the space formed with the press mold closed, the glass is insufficiently filled in the space, and the surface accuracy of the optical function surface is reduced. The portion that should become the positioning reference surface of the glass does not reach the mold member, and the positioning reference surface is not formed.

  Therefore, in order to enable a method of forming the optical function surface and the positioning reference surface in a lump, it is desired to use a preform having a high volume accuracy, that is, a mass accuracy.

  As described above, as a method for producing a glass preform with high productivity, a method in which molten glass is discharged, a molten glass lump having a desired mass is separated, and the preform is formed in the process of cooling the glass lump. (Patent Document 2). If a preform is produced using this method, the optical element can be mass-produced with extremely high productivity starting from melting of glass. However, as described above, it is necessary to precisely control the volume of the preform. However, in the conventional glass preform production method, there is a slight variation in the volume of the preform. However, the volume control of the preform was not always sufficient.

  The present invention has been made in order to solve the above-described problems, and is a glass preform lot configured by a plurality of relatively lightweight preforms suitable for precision press molding of a small optical element. An object of the present invention is to provide a glass preform lot in which the volume variation between the preforms is very controlled. Another object of the present invention is to provide a method for producing a preform lot from molten glass in which the volume variation between the preforms is extremely controlled. In addition, the present invention is a glass molded product lot in which a plurality of glass molded products that are preform base materials from molten glass are collected, and the glass molded product lot in which the volume variation between the glass molded products is extremely controlled. A method for producing, a method for producing a preform from a glass molded body of the glass molded body lot, and a method for manufacturing an optical element for producing an optical element by precision press molding each preform of the preform lot. Objective.

The present invention for solving the above problems is as follows.
[1] In a glass preform lot consisting of a plurality of glass preforms for precision press molding, it is composed of a spherical preform made of glass whose SiO ₂ content is limited to a range of 0 to 20% by mass. A glass preform lot having an average mass of 200 mg or less and a mass tolerance ratio with respect to the mass within ± 0.3%.
[2] Described in [1], which is composed of a preform made of any one of SiO ₂ -containing glass, glass containing B ₂ O ₃ and La ₂ O ₃ , phosphate glass, and fluorophosphate glass. Glass preform lots.
[3] The glass preform lot according to [1] or [2], comprising a preform made of glass having a specific gravity of 3.3 or more.
[4] Glass in which the content of SiO ₂ is limited to a range of 0 to 20% by mass in a preform base material lot consisting of a plurality of preform base materials for processing into a glass preform for precision press molding A preform base material lot having an average mass of 200 mg or less composed of a spherical preform base material and having a mass tolerance ratio with respect to the mass within ± 0.3%.
[5] SiO ₂ -containing glass, glass containing B ₂ O ₃ and La ₂ O ₃ , composed of a preform base material made of any one of glass of phosphate glass and fluorophosphate glass [4] The preform base material lot described in 1.
[6] The preform matrix lot according to [4] or [5], which is composed of a preform matrix made of glass having a specific gravity of 3.3 or more.
[7] A glass made of a plurality of glass preforms by repeating a step of dropping a predetermined amount of glass droplets from the outlet of the outflow nozzle and forming the obtained glass droplets into a glass preform for precision press molding. In the production method of a glass preform lot for producing a preform lot made of glass, a glass drop made of glass having a SiO ₂ content in the range of 0 to 20% by mass is dropped, and the dropped glass has a mass of 200 mg. The method for producing a glass preform lot, wherein the glass preform lot is produced by molding into a spherical preform having a mass tolerance ratio within ± 0.3% with respect to the mass.
[8] In a method for producing a glass molded product lot, a process of producing a plurality of glass molded product lots by repeating a step of forming a glass droplet of a predetermined mass by dropping a glass droplet having a predetermined mass from an outlet of the outflow nozzle. A glass drop made of glass having a content of SiO ₂ in the range of 0 to 20% by mass is dropped, and the dropped glass is molded into a spherical glass molded body having a mass of 200 mg or less. The method for producing a glass molded body, wherein a glass molded body lot having a ratio within ± 0.3% is produced.
[9] A glass preform for producing a glass preform to be subjected to precision press molding having the same diameter by polishing the entire surface of each glass molded body of the glass molded body lot produced by the method according to [8] Manufacturing method.
[10] A glass preform taken out from the glass preform lot according to any one of [1] to [3], or taken out from a glass preform lot produced by the method according to [7] or [9] A method of manufacturing an optical element in which a glass preform is heated and precision press molding is performed using a press mold.
[11] Precise press molding of a glass preform using a press mold is performed by filling the glass into a sealed space formed with the press mold closed. Manufacturing method.
[12] The method for producing an optical element according to [11], wherein a precision press-molded product having a ridge composed of a free surface is formed.
[13] The method for manufacturing an optical element according to any one of [10] to [12], wherein at least two or more positioning reference surfaces are formed by precision press molding.

  ADVANTAGE OF THE INVENTION According to this invention, the glass preform lot suitable for manufacture by the precision press molding of a small optical element and a small mass variation can be provided.

  Furthermore, according to the present invention, it is possible to produce a glass preform lot that is lightweight and has a small mass variation that is suitable for manufacturing a small optical element by precision press molding.

  According to the present invention, a glass compact having a light weight and a small mass variation suitable for manufacturing a small optical element by precision press molding, in particular, a glass having a small mass variation that is finished into a glass preform for precision press molding by polishing. A lot of compacts can be produced. Further, by polishing the glass molded body, a glass preform with small mass variation can be mass-produced.

  According to the present invention, an optical element, in particular, an optical element having a positioning reference surface composed of a mold transfer surface, which is small or small, can be mass-produced efficiently by using the preform having the small mass variation.

  As described above, it is preferable that a small optical element incorporated in a small device incorporating an image pickup device such as a camera-equipped mobile phone includes an optical functional surface and a positioning reference surface formed together by precision press molding. As described above, when such an optical element is precision press-molded, the volume of the glass preform must be precisely controlled.

  As the optical element molding preform, one having a mass of 200 mg or less is suitable. A mass tolerance within ± 0.3% is required for the preform used when the optical functional surface and the positioning reference surface of the optical element are formed together by precision press molding.

  For the production of the preform, a method of flowing out molten glass and separating molten glass droplets of a target mass is suitable because high productivity is obtained. Specifically, a method of dropping the molten glass flowing down through the nozzle from the nozzle outlet and forming the obtained glass droplet on a preform is suitable. The mass of the glass droplet is determined by the downward acceleration acting on the glass hanging from the nozzle outlet, the outer diameter of the lower end of the nozzle, the surface tension of the molten glass, and the like. Therefore, if these conditions are made constant, it becomes possible to continue dropping glass drops having a constant mass.

  However, if it is attempted to reduce the ratio of the mass tolerance to the target preform mass, it is difficult to suppress the mass variation only by maintaining the above-mentioned conditions constant. When a high-speed camera is used to shoot a glass drop dripping from the nozzle outlet, first, a constriction occurs between the molten glass that hangs down and the molten glass that is about to flow out of the outlet, and the constriction gradually narrows and extends longer. The lower end is lowered. When the constriction is thin and long, the glass is torn at the thread-like portion, and the glass above the torn portion returns to the vicinity of the nozzle outlet due to surface tension, and becomes glass that hangs down to the nozzle outlet. On the other hand, the glass below the broken portion is taken into the separated glass droplets.

  When observed more closely, it was found that the tearing position fluctuated each time the glass was dropped. When the tearing position becomes higher, the amount taken into the glass drop in the thread-like part increases, the mass of the glass drop slightly increases, and when the tearing position becomes lower, the amount taken into the glass drop among the thread-like part decreases, The glass drop mass is slightly reduced. This mass variation has been found to increase mass tolerances.

  As a result of further detailed analysis, if the filamentous part is long, the tearing position is likely to fluctuate, and as a result, the mass fluctuation of the glass droplet tends to be large, and if the filamentous part is broken, the mass fluctuation of the glass drop is small. I found out. It was also found that the glass determines whether the filamentous portion is long or short under the condition of preventing devitrification when the glass flows out.

Furthermore, when examined using various glass compositions, the main factor that determines the length of the filamentous part is the content of SiO _{2 in} the glass. If the amount of SiO ₂ exceeds a certain level, the filamentous part becomes longer. It was also found that when the amount is small, the filamentous portion is shortened. That is, if the amount of SiO ₂ is limited, the length of the thread-like portion at the time of dropping can be shortened to such an extent that it is not easily disturbed, and the mass fluctuation of the glass droplet can be suppressed to a small value.

  As described above, a preform used for a small optical element or the like built in a mobile device is required to be lightweight and have high mass accuracy. When assembling an imaging optical system by aligning small optical elements, the optical axes of multiple small optical elements are precisely aligned, and the distance between each element and the distance from the imaging element are accurately maintained. When a holder for positioning and fixing is used, assembly work is facilitated. If each element is fitted in the holder, accurate alignment and assembly can be performed without adjusting positioning. For this purpose, it is desired to form at least two positioning reference surfaces on the optical element together with the optical functional surface by precision press molding. In such precision press molding, it is necessary to fill a space called a cavity surrounded by a press mold without excess or deficiency. If the volume of the preform is too small, the glass will enter the clearance between the mold members that make up the press mold during press molding, forming a molding burr and stopping the precision press molding process. There is a risk of damaging the molded product or the molding surface. Conversely, if the volume of the preform is insufficient, the glass will be insufficiently filled in the cavity, resulting in insufficient transfer of the optical function surface and positioning reference surface, and the desired purpose cannot be achieved. Such a problem is likely to become more prominent as the target optical element is smaller.

Therefore, in order to prevent the preform mass from being excessive or insufficient, the present invention constitutes a preform with a glass preform lot having an average mass of 200 mg or less and a mass tolerance with respect to the mass within ± 0.3%. It is provided by limiting the amount of SiO ₂ in the glass to be a predetermined amount or less. Based on the above findings, the present inventor completed the present invention by experimentally finding an appropriate SiO ₂ content with respect to the average mass and mass tolerance.

That is, the present invention relates to a spherical preform made of glass in which the content of SiO ₂ is limited to a range of 0 to 20% by mass in a glass preform lot made of a plurality of glass preforms used for precision press molding. Is a glass preform lot having an average mass of 200 mg or less and a mass tolerance with respect to the mass within ± 0.3%.

  Here, the preform lot means a set of a plurality of preforms made of the same kind of glass and having the same shape and mass. For example, when mass-producing a predetermined optical element, prepare a preform lot consisting of a required number of preforms, take out the preform from the lot, and perform precision press molding using a press mold of the same shape Thus, optical elements having the same shape can be mass-produced. At this time, a plurality of sets of press molds may be used, or the preforms may be precision press molded one after another using one press mold set. A preform lot can be considered to be composed of a plurality of preform lots. For example, a lot composed of 1000 preforms can be considered to be composed of 10 lots composed of 100 preforms, or 100 lots composed of 10 preforms. It can be considered that it is constituted by. In a preferred embodiment of the present invention, the number of preforms constituting a lot is 500 or more, preferably 1000 or more, more preferably 2000 or more, and further preferably 5000 or more. The upper limit of the number may be determined by the required number of optical elements.

  Whether a preform lot has a mass tolerance ratio within ± 0.3% of the average mass of the preforms constituting the preform lot should be verified by a preform lot consisting of 500 preforms. Can do. When the preform lot consists of 500 preforms, the ratio of the mass tolerance to the average mass is preferably within ± 0.29%, more preferably within ± 0.28%. Further, even if the number of preforms constituting the preform lot is 500 or more, the ratio of the mass tolerance to the average mass is preferably within ± 0.3%, and preferably 1000 pieces as described above. As described above, even when the number is 2000 or more, and more preferably 5000 or more, the ratio of the mass tolerance to the average mass is preferably within ± 0.3%.

  A preferred embodiment of the present invention is a glass preform lot comprising a preform for precision press molding an optical element having a surface formed by transferring a molding surface of a press mold during precision press molding and a free surface. It is.

  The optical element made by the preform of the present invention has a positioning reference surface in addition to the optical functional surface. For example, the lens positioning reference surface is a reference surface for determining the distance between the lenses and a reference surface for accurately matching the optical axes of the lenses. By bringing these reference surfaces into contact with the holder, each lens can be accurately aligned. Taking a lens as an example, a bowl-shaped flat portion is formed so as to surround each lens surface, and the two bowl-shaped flat portions of the two lens surfaces are parallel to each other. The one hook-shaped flat portion is used as a positioning reference surface and is in contact with the holder. A pressure for maintaining the abutted state is applied to the other bowl-shaped flat surface to fix the lens to the holder. With such a lens, the distance between the two bowl-shaped flat portions (referred to as edge thickness) is short (edge thickness) without causing damage to the lens during molding and without causing damage to the lens when fixed to the holder. It is desirable to reduce the thickness. In such a lens, a side surface between two bowl-shaped flat portions, that is, a portion called an edge is used as a second positioning reference surface. The second positioning reference surface is a reference surface for aligning the optical axis of the lens. Therefore, the edge is a surface to which a press mold forming surface is transferred during precision press molding. The press mold member transferred to the edge is a member called a sleeve mold or a barrel mold. A sleeve mold used when molding a small optical element has an elongated through hole into which an upper and lower molds are inserted. A part of the inner surface of the through hole becomes a molding surface transferred to the edge. The upper and lower mold surfaces are provided with a release film that improves the mold releasability of the glass, but it is difficult to provide a release film with a uniform thickness on the inner surface of the through hole of the sleeve mold. No release film is formed. Therefore, in order to prevent the glass from fusing to the inner surface of the sleeve mold through-hole during press molding, the edge area should be reduced as long as the glass is not damaged, and the contact area between the glass and the sleeve mold should be minimized. .

  For this reason, the edge thickness is reduced, but when a lens with a thin edge thickness is precision press-molded, the glass is filled from the portion that becomes the lens surface and gradually spreads in the sleeve mold direction. At this time, since the volume of the space between the upper mold forming surface and the lower mold forming surface for transferring and molding the two bowl-shaped flat portions is small, if the amount of the glass constituting the preform is too small, If the amount of the glass is small or small, the glass does not reach the sleeve mold even when pressed, and an edge serving as a positioning reference surface is not formed.

  That is, in the preform for molding the optical element, over 200 mg or less of the mass is allowed to be within a range of ± 0.3%. Therefore, in the present invention, the average mass of the preforms constituting the lot is 200 mg or less, preferably 150 mg or less, more preferably 1 to 140 mg, and the mass tolerance is within ± 0.3%, preferably within ± 0.2%. More preferably, it is within ± 0.11%, further preferably within ± 0.10, and even more preferably within ± 0.09.

  Here, the average mass is an arithmetic average value (Mav) calculated from the mass of each preform. The mass tolerance is ± (Mmax−Mmin) from the mass of the preform having the largest mass (referred to as Mmax) and the mass of the preform having the smallest mass (referred to as Mmin) in the preforms constituting the lot. This is a value calculated by the formula / 2Mav.

  When the number of preforms constituting a lot is large, a predetermined number of preforms may be randomly extracted from the lot, and Mav, Mmax, and Mmin may be obtained using the extracted preforms.

  Next, the glass constituting the preform will be described in detail. Unless otherwise specified, the glass component content is expressed in mass%.

As described above, the inventors' experiments have revealed that the length of the filamentous portion of the molten glass is determined by the amount of SiO ₂ in the glass. When the content of SiO ₂ exceeds 20%, the thread-like portion becomes long, and the separation is likely to be influenced by the external environment. On the other hand, by limiting the content of SiO ₂ to the range of 0 to 20%, it is difficult for the separation location to vary due to the external environment, and a lot made of a lightweight preform with a small mass tolerance can be obtained. A preferred range for the amount of SiO ₂ is 0 to 17%, a more preferred range is 0 to 15%, a further preferred range is 0 to 12%, a still more preferred range is 0 to 10%, a still more preferred range is 0 to 9%. It is.

Examples of the glass in the present invention include SiO ₂ -containing glass, B ₂ O ₃ and La ₂ O ₃ -containing glass, phosphate glass, and fluorophosphate glass.
The SiO ₂ containing _{glass, SiO 2 1~20%, B 2} O 3 0~65%, Li 2 O 0~12%, Na 2 O 0~12%, K 2 O 0~12%, MgO 0~ 30%, CaO 0-30%, SrO 0-30%, BaO 0-30%, ZnO 0-40%, La ₂ O ₃ 0-50%, Gd ₂ O ₃ 0-40%, Y ₂ O ₃ 0 _{~20%, ZrO 2 0~15%,} TiO 2 0~20%, Ta 2 O 5 0~30%, WO 3 0~20%, can be exemplified glass containing Nb ₂ O ₅ 0~30% it can.
Among these glasses, those suitable for precision press molding are glasses having a total content of Li ₂ O and ZnO of 1% or more, and glass having a glass transition temperature of 610 ° C. or less is preferable.

As glass containing B ₂ O ₃ and La ₂ O ₃ , SiO ₂ 0-20%, B ₂ O ₃ 1-65%, Li ₂ O 0-12%, Na ₂ O 0-12%, K ₂ O 0-12%, MgO 0-30%, CaO 0-30%, SrO 0-30%, BaO 0-30%, ZnO 0-40%, La ₂ O ₃ 1-50%, Gd ₂ O ₃ 0 _{~40%, Y 2 O 3 0~20} %, ZrO 2 0~15%, TiO 2 0~40%, Ta 2 O 5 0~30%, WO 3 0~20%, Nb 2 O 5 0~45 %, Bi ₂ O ₃ 0-45% glass can be exemplified.
Among these glasses, those suitable for precision press molding are glasses having a total content of Li ₂ O and ZnO of 1% or more, and glass having a glass transition temperature of 630 ° C. or less is preferable.

Examples of the phosphoric acid _{glass, P 2 O 5 1~50%,} SiO 2 0~20%, B 2 O 3 0~35%, Li 2 O 0~12%, Na 2 O 0~12%, K 2 O 0~12%, 0~30% MgO, CaO 0~30%, SrO 0~30%, BaO 0~30%, 0~40% ZnO, La 2 O 3 0~20%, Gd 2 O 3 0~ 20%, Y ₂ O ₃ 0-20%, ZrO ₂ 0-15%, TiO ₂ 0-30%, Ta ₂ O ₅ 0-20%, WO ₃ 0-20%, Nb ₂ O ₅ 0-45% , Bi ₂ O ₃ 0-45% glass can be exemplified.
In this glass, the amount of Li ₂ O is preferably 0.1% or more from the viewpoint of lowering the glass transition temperature and lowering the temperature during press molding.

As fluorophosphate glass, P ⁵⁺ 5-50%, Al ³⁺ 0.1-30%, Mg ²⁺ 0-20%, Ca ²⁺ 0-25%, Sr ²⁺ 0 in terms of cation%. -30%, Ba2 ⁺ 0-30%, Li ⁺ 0-30%, Na ⁺ 0-10%, K ⁺ 0-10%, Y3 ⁺ 0-10%, La3 ⁺ 0-5%, Gd ³⁺ containing 0 to 5%, F ^- and O ^2-F to the total amount of ^- content, i.e. the molar ratio ^F - / - glass ^(F + O ^2-) is 0.25 to 0.95 Can be illustrated. This fluorophosphate glass is suitable for realizing low dispersion characteristics.

Moreover, copper-containing fluorophosphate glass can be illustrated as another fluorophosphate glass. This glass has a near-infrared absorption function, and becomes a material of an optical element having a color sensitivity correction function of a semiconductor imaging element such as a CCD or a CMOS. Although the copper-containing phosphate glass can be exemplified as the glass having the same function, the copper-containing fluorophosphate glass is superior to the copper-containing phosphate glass in terms of weather resistance. Copper-containing glass constituting the color sensitivity correction element of the semiconductor imaging device having a near infrared absorbing function, since the melting temperature is too high Cu ²⁺ in the glass is being reduced Cu ^+, the color sensitivity correction function descend. Since the melting temperature increases as the amount of SiO ₂ increases, it is more preferable that the copper-containing glass does not contain SiO ₂ .

In each glass, the amount of SiO ₂ is 0 to 20%, and the preferable range of the content of SiO ₂ is as described above. The glass phosphate, fluorophosphate glass is more preferably free of SiO _2.
If the amount of SiO ₂ is about the same, glass with a higher specific gravity will separate the molten glass without lengthening the filamentous portion, so the specific gravity of the glass constituting the preform should be 3.3 or higher. Is preferably 3.4 or more.

In the case of glass containing B ₂ O ₃ and La ₂ O ₃ and phosphate glass, La ₂ O ₃ , Gd ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Nb ₂ O ₅ , from the viewpoint of increasing specific gravity, The total amount of Ta ₂ O ₅ , WO ₃ , TiO ₂ and Bi ₂ O ₃ is preferably 20% or more, more preferably 25% or more, and further preferably 30% or more.

The shape of each preform constituting the lot is a sphere. When a small optical element is precision press-molded, if a spherical preform is used, if the lower mold molding surface is concave, the preform can be stably disposed at the center of the molding surface. In addition, the glass in which the amount of SiO ₂ is limited to 20% or less has a strong tendency to become a sphere due to surface tension in the state of glass droplets, and has the feature that it is easy to form a preform in a shape close to a true sphere Have.

  Up to this point, the preform lot has been described. Hereinafter, a preform base material lot composed of a plurality of preform base materials for processing into a glass preform used for precision press molding will be described.

Preform preform lot of the present invention, the preform preform lot comprising a plurality of preform preform for processing into glass preform to be subjected to precision press molding, the content of SiO ₂ 0 to 20 wt% A preform base material lot having an average mass composed of a spherical preform base material made of glass limited to the range of 200 mg or less and a mass tolerance ratio with respect to the mass within ± 0.3%.

  The preform base material lot is a set of a plurality of preform base materials. The concept of the lot is the same as the concept of the lot in the preform lot. The preform base material can be formed into a preform by machining (for example, polishing) the surface thereof. At that time, if the preform base material lot of the present invention is used and the amount of glass removed by machining is equalized for each preform base material, a lot consisting of preforms of equal mass, that is, the preform lot of the present invention, Obtainable.

The preform base material is produced by dropping glass drops as in the above-described preform. However, the phenomenon described above also occurs in dropping glass drops when forming the preform base material, and the thread-like portion becomes longer. Whether or not the mass fluctuation of the base material becomes large depends on the amount of SiO _{2 in} the glass. Except for whether preform preforms and preforms are finished into preforms by processing, manufacturing method, preferred glass composition, specific gravity, number of preforms constituting lot (number of preforms constituting lot) The preferred ranges of the average mass and the ratio of the mass tolerance to the average mass are also common.

Next, a production method for glass preform lots (a mass production method for glass preforms) will be described.
The method for producing a glass preform lot according to the present invention includes a step of dropping a glass drop of a predetermined mass from the outlet of the outflow nozzle and molding the obtained glass drop into a glass preform for precision press molding. In the production method of a glass preform lot, producing a glass preform lot consisting of a plurality of glass preforms,
A glass drop made of glass having a content of SiO ₂ in the range of 0 to 20% by mass is dropped, and the dropped glass is formed into a spherical preform having a mass of 200 mg or less, and the ratio of mass tolerance to the mass Is a method for producing a glass preform lot, wherein the glass preform lot is produced within a range of ± 0.3%.

  First, a molten glass obtained by heating, melting, clarifying and homogenizing a glass raw material is introduced into a pipe at the lower end of the pipe by flowing through the pipe from a container for storing the molten glass. Although the molten glass flows out from the glass outlet at the lower end of the nozzle, the temperature of the pipe and the nozzle is controlled so that the amount of glass flowing out per unit time becomes constant.

  The molten glass that has flowed out of the glass outlet port hangs down to the lower end of the nozzle due to surface tension. When the downward force acting on the glass that hangs down becomes stronger than the force at which the molten glass stays at the lower end of the nozzle, the molten glass drops from the lower end of the nozzle. Here, since the glass outflow amount per unit time is made constant, dripping of the molten glass occurs at a constant cycle. The mass of the molten glass droplet is obtained by multiplying the glass outflow amount per unit time expressed by mass by the period.

  A mold having a recess is carried under the nozzle, receives a glass drop dripping on the outer peripheral surface of the recess, is introduced into the recess by rolling or sliding, and the recess is formed by a gas jetted upward from a gas outlet provided at the bottom of the recess. The glass drops are moved up and down to form a spherical preform. For mass production of preforms, a plurality of molds are prepared, and the molds are successively carried under the nozzle to receive glass droplets. The molds that have received the glass droplets are unloaded from the nozzles and empty molds are used as nozzles. Carry it down to prepare for dropping glass drops. The preform with the glass droplets is moved to form a preform in the recess and cooled to a temperature range where the preform does not deform. Then, the preform is taken out from the mold and is again placed below the nozzle as an empty mold. Carry in. Preforms are mass-produced by performing such steps one after another for each of a plurality of molds. The preform mass-produced product obtained here corresponds to a preform lot.

  Next, a production method of a glass molded product lot (a mass production method of a glass molded product) will be described. Examples of the glass molded body include the preform and preform preform.

The method for producing a glass molded product lot according to the present invention produces a plurality of glass molded product lots by repeating a step of dropping a glass drop of a predetermined mass from the outlet of the outflow nozzle and molding the obtained glass droplet, In the production method of glass molded body lots,
A glass drop made of glass having a content of SiO ₂ in the range of 0 to 20% by mass is dropped, and the dropped glass is molded into a spherical glass molded body having a mass of 200 mg or less. It is the said glass molded object production method which produces the glass molded object lot within a ratio of +/- 0.3%.

  When the glass molded body is a preform, it is the same as the above-described preform production method. When the glass molded body is a preform base material, a preform base material lot can be produced according to the present invention. In that case, it is possible to manufacture a glass preform to be used for precision press molding of the same diameter by polishing the entire surface of the glass molded body. By performing this polishing process on the preform base material lot, a glass preform is obtained. Remodeling lots can be produced.

The composition, specific gravity, and other properties of the glass constituting the glass molded body are the same as those of the aforementioned preform.
In addition, if there are defects such as scratches and dirt on the preform surface, it may cause defects in the optical element, so it is appropriate to finish the preform surface to a smooth surface so that scratches do not remain on the preform surface. . Further, after the polishing is completed, the preform is washed to make a clean surface so that no abrasive remains.

Next, a method for manufacturing an optical element will be described.
The method for producing an optical element of the present invention comprises heating a glass preform taken out from each glass preform lot or a glass preform prepared by each of the above methods, and precision press molding using a press mold. This is a method for manufacturing an optical element.

  The preforms to be taken out are all spherical preforms having a mass that precisely matches the target mass, and therefore have a surface composed of a surface formed by transferring a molding surface of a press mold during precision press molding and a free surface. A small optical element can be manufactured stably.

  Precision press molding is a method that uses a press mold including an upper mold, a lower mold, and a sleeve mold, presses the preform by heating, and accurately transfers the shape of the molding surface of the press mold to glass. is there. For the processing of the mold material of the press mold and the material of the mold material, the mold release film formed on the molding surface of the upper mold and the lower mold, the method of forming the mold release film, the type of atmosphere for performing the precision press molding, etc., apply known techniques. That's fine.

  For example, a surface formed by using a press mold having an upper mold, a lower mold, and a sleeve mold, transferring each molding surface of the upper mold, the lower mold, and the sleeve mold to glass and transferring the upper mold molding surface. And the ridge formed by the surface formed by transferring the sleeve molding surface and / or the ridge formed by the surface formed by transferring the lower mold surface and the surface formed by transferring the sleeve molding surface to the free surface Press molding to mass produce optical elements with the same shape.

As an example of the precision press molding method, a spherical preform is placed in the center of the concave lower mold surface inserted into the through hole of the sleeve mold, and the upper mold is placed so that the molding surface faces the lower mold surface. Insert into the sleeve-type through hole. In this state, when the preform and the press mold are heated together and the temperature of the glass constituting the preform rises to a temperature showing a viscosity of 10 ⁶ dPa · s, the upper mold and the lower mold are pressed. Pressurize the reform. The pressurized preform is spread out in a space (called a cavity) surrounded by the upper mold, the lower mold, and the sleeve mold. In this manner, the glass preform is pressed in the cavity, and the glass is filled into the cavity which is a sealed space formed in a state where the press mold is closed.

  The relative positions of the molding surfaces of the upper mold, the lower mold, and the sleeve mold in the mold closed state, and the angle formed by the surface normal are precisely formed. If the above molding is performed using such a press mold, the optical function surface and the positioning reference surface can be formed with a highly accurate positional relationship and angle.

  In the case of the molding of the lens shown in FIG. 3, for example, the central portion of the upper mold molding surface is a lens surface that is an optical functional surface of the lens, and the peripheral portion is a ring-shaped shape that is transfer-molded with a bowl-shaped flat portion. A plane. Similarly, for the lower mold forming surface, the center portion is a surface on which the lens surface is transfer-molded, and the peripheral portion is the plane on the annular zone on which the bowl-shaped flat portion is transfer-molded. Until the press molding is completed, the upper and lower molds are accurately maintained so that the directions of the upper and lower molds face each other and the central axes of the upper and lower molds coincide with each other.

  By filling glass in a sealed space formed with the press mold closed, the inner surface of the sleeve mold through-hole is transferred to the glass. By accurately forming the angle between the central axis of the sleeve-type through hole and the inner surface of the through-hole, and maintaining the central axis of the through-hole and the upper and lower mold center axes precisely until the end of press molding, 3, the two lens surfaces 10 and 11, the two flange-shaped flat portions 7 a and 7 b, the relative position of the edge 6 of the lens on which the inner surface of the sleeve mold is transferred, and the angle formed by the surfaces of each other. It can be formed accurately. Then, one of the two hook-shaped flat portions and the edge are used as a positioning reference surface, and one of the hook-shaped flat portions is used as a reference surface for accurately positioning the distance between the lenses, and the edge is used as the light between the lenses. It can be used as a reference plane for precisely matching the axes.

  In order to prevent the inner surface of the sleeve-type through-hole from being fused to the glass, the mass of each preform is accurately determined relative to the mass of the target lens even if the edge thickness is reduced within a range where the lens is not damaged. Therefore, the inner surface of the sleeve-type through-hole can be transferred to form an edge that functions as a positioning reference surface, and a molding burr does not occur and the optical element mass production process is not stopped.

  In addition, it is desirable to form ridges 9a and 9b where the edge 6 and the bowl-shaped flat portions 7a and 7b intersect with each other on the free surface. If the edge and bowl-shaped flat part are formed, there is no risk of hindering the positioning function. It may cause dust generation. When dust adheres to the light-receiving surface of the image sensor, the image quality is greatly reduced. Therefore, in order to prevent such trouble, it is desirable to mold a precision press-molded product having a ridge composed of a free surface.

In the optical element, it is desirable to form at least two or more surfaces, specifically, two or three positioning reference surfaces by precision press molding. The two or three positioning reference surfaces are preferably formed non-parallel to each other. If the optical element is positioned using two reference planes that are not parallel to each other in this way, the positioning and orientation of the optical element in the optical system can be determined with high accuracy. An optical element having rotational symmetry like a lens only needs to have two reference surfaces. In the case of an optical element having no rotational symmetry such as a prism, three positioning reference planes are formed to accurately determine the positioning in the optical system and the orientation at that position.
An optical multilayer film such as an antireflection film may be formed on the thus produced optical element as necessary.

Examples will be described.
Example 1
First, glass raw materials are weighed and prepared so as to obtain optical glasses A and B having an SiO ₂ amount of 20% by mass or less shown in Table 1, and sufficiently stirred, introduced into a melting vessel, heated and melted. Clarified and stirred to prepare a homogeneous molten glass. A glass preform was produced from molten glass droplets using the apparatus shown in FIG.

The pipe 1 connected to the bottom of the melting vessel is opened, and the molten glass flows out from the nozzle 2 attached to the lower end of the pipe at a constant flow rate. The nozzle, the pipe, and the melting vessel are each temperature controlled so that the glass does not devitrify and has a viscosity that provides a desired flow rate.
As shown in FIG. 1, a gas flow path forming cover 3 is provided at the lower end of the pipe 1 and the outer periphery of the nozzle 2, and a gas flow for flowing gas into the space between the gas flow path forming cover and the pipe and nozzle. A path 4 is provided. And the opening part 3-1 is provided in the lower end of the cover for gas flow path formation, and the nozzle front-end | tip protrudes from the said opening part. The nozzle, the gas flow path forming cover, and the gas flow path forming cover opening are preferably arranged symmetrically around the central axis of the nozzle. In addition, it is desirable that the gas discharged from the gas channel forming cover opening also flow evenly around the central axis.

In this embodiment, the outflow amount of the glass is controlled by adjusting the inner diameter of the pipe, the inner and outer diameters of the nozzle, and the temperature of the pipe and the nozzle so that the molten glass hanging from the lower end of the nozzle falls at a constant cycle. The molten glass flowing out from the glass outlet hangs down to the lower end of the nozzle, but the gas that continuously spouts downward from the gas channel forming cover opening at a constant flow rate is sprayed on the molten glass. Wind pressure is applied.
A high-frequency induction coil (not shown) is disposed so as to surround the outer periphery of the nozzle, and a high-frequency current is passed to heat the nozzle with high-frequency induction.
The fall of the molten glass occurs when the gravity acting on the molten glass droops more than the force at which the molten glass stays at the lower end of the nozzle. However, with this method, only glass droplets having a mass determined by the force of staying at the lower end of the nozzle can be obtained, and lighter glass droplets cannot be dropped.
However, according to the present embodiment, the molten glass drooping receives a downward force due to the wind pressure caused by the gas, and accordingly, a lighter glass drop can be obtained. Then, if the gas flow rate is controlled by a mass flow controller or the like so that the gas flow rate becomes constant, the mass of the glass droplet can be stabilized.

  The molten glass droplet is received by the molding die 5 waiting under the nozzle. A vertical cross section of the mold 5 is shown in FIG. A glass drop dripped is received at the glass drop receiving surface 5-1 of the mold. Since the glass droplet receiving surface 5-1 is also inclined in the direction of the concave portion 5-2 provided on the upper surface of the mold, the glass droplet slides or rolls from the receiving surface 5-1 into the concave portion 5-2.

  As shown in FIG. 2, the cross section of the concave portion 5-2 has a shape that spreads in a trumpet shape from the bottom to the top, and one gas jet port for jetting gas upward is provided at the bottom of the concave portion. The glass drop introduced into the recess descends while rolling on the inner wall of the recess toward the bottom of the recess. However, since the inner diameter of the recess decreases, the glass drop is strongly subjected to upward wind pressure as it falls. It will be. As a result, the glass droplet rises in the recess, but when it rises, the upward wind pressure is weakened, so that it drops while rolling along the inner wall of the recess. Then, since the upward wind pressure is strongly received again, the movement of the glass droplet ascending in the recess and descending while rolling on the inner wall of the recess is repeatedly performed in a short time. Since the direction in which the glass droplet rolls on the inner wall of the concave portion is random, the glass droplet is cooled while being spheroidized as the above movement is repeated, and formed into a spherical preform. When the temperature reaches a temperature at which the preform is not deformed by cooling, the preform in the recess is taken out and cooled to room temperature at a speed at which the glass does not break.

  By repeating the above steps using a plurality of molds, it is possible to mass produce spherical preforms of equal mass. In this way, a preform lot made of a spherical preform having a desired mass made of optical glass and a small mass tolerance was obtained. Table 1 shows the glass used, the number of preforms obtained, the average mass, mass tolerance, and diameter.

(Example 2)
A spherical preform base material was mass-produced in the same manner as in Example 1. Table 1 shows the glass used, the number of base materials obtained, the average mass, the ratio of the mass tolerance to the average mass, the mass tolerance, and the diameter. These preform preforms were annealed to reduce strain and then polished to obtain preform lots having a value equivalent to the ratio of mass tolerance to the average mass of the preform preform.

(Example 3)
Using the preform lots obtained in Examples 1 and 2, small aspherical lenses having a cross-sectional shape shown in FIG. 3 were obtained by precision press molding. None of the lenses were damaged, and the lens had sufficient optical performance. Further, the edge 6 and the bowl-shaped flat part 7 of each lens were obtained by transferring the press-molding molding surface, and the ridge where the edge and the bowl-shaped flat part intersected was a rounded free surface. And generation | occurrence | production of the shaping | molding burr | flash was not recognized.

  These aspherical lenses function as lenses constituting an imaging optical system of an imaging device built in a mobile phone. The lens obtained in this way and a lens with an edge and a bowl-shaped flat part as a positioning reference surface produced in exactly the same way except for the shape are assembled in the lens holder and fixed with the positioning reference surface in contact with the holder By doing so, each lens could be accurately arranged in the holder.

[Comparative example]
Using the glass having a SiO ₂ content of 46% by mass shown in Table 1 and producing the preform shown in Table 1, the mass tolerance was large and the mass was varied.
Using this lot, a small aspherical lens is precision press-molded by the same method as described above, and the entire edge becomes a free surface and does not function as a positioning reference surface. Troubles such as no longer sliding occurred.

Explanatory drawing of the apparatus which produces a glass preform from a molten glass drop. The vertical sectional view of the shaping | molding die for producing a glass preform from a molten glass drop. Sectional explanatory drawing of the lens which is 1 aspect of the optical element of this invention.

Claims (13)

In glass preform lots consisting of multiple glass preforms for precision press molding,
Glass having an average mass of 200 mg or less composed of a spherical preform made of glass whose SiO ₂ content is limited to a range of 0 to 20% by mass, and a mass tolerance ratio with respect to the mass within ± 0.3%. Preform lot made. The glass product according to claim 1, which is made of a preform made of any one of SiO ₂ -containing glass, glass containing B ₂ O ₃ and La ₂ O ₃ , phosphate glass, and fluorophosphate glass. Preform lot.   The glass preform lot according to claim 1 or 2, comprising a preform made of glass having a specific gravity of 3.3 or more. In preform preform lots consisting of multiple preform preforms for processing into glass preforms for precision press molding,
The average mass composed of a spherical preform made of glass whose SiO ₂ content is limited to the range of 0 to 20% by mass is 200 mg or less, and the ratio of mass tolerance to the mass is within ± 0.3%. Preform base material lot. 5. The preform according to claim 4, comprising a preform base material made of any one of glass containing SiO _2, glass containing B ₂ O ₃ and La ₂ O ₃ , phosphate glass, and fluorophosphate glass. Preform base material lot.   The preform preform lot according to claim 4 or 5, wherein the preform preform lot is composed of a preform preform made of glass having a specific gravity of 3.3 or more. A glass preform comprising a plurality of glass preforms by repeating a step of dropping a glass drop of a predetermined mass from the outlet of the outflow nozzle and forming the obtained glass droplet into a glass preform for precision press molding. In the production method of glass preform lots that produce lots,
A glass drop made of glass having a content of SiO ₂ in the range of 0 to 20% by mass is dropped, and the dropped glass is formed into a spherical preform having a mass of 200 mg or less, and the ratio of mass tolerance to the mass A method for producing a glass preform lot, wherein a glass preform lot is produced within a range of ± 0.3%. In a method for producing a glass molded product lot, a plurality of glass molded product lots are produced by repeating a step of molding a glass droplet obtained by dropping a glass drop of a predetermined mass from the outlet of an outflow nozzle.
A glass drop made of glass having a content of SiO ₂ in the range of 0 to 20% by mass is dropped, and the dropped glass is molded into a spherical glass molded body having a mass of 200 mg or less. The method for producing a glass molded body, wherein a glass molded body lot having a ratio within ± 0.3% is produced.   A method for producing a glass preform for producing a glass preform to be subjected to precision press molding having the same diameter by polishing the entire surface of each glass molded body of a glass molded body lot produced by the method according to claim 8. .   A glass preform taken out from the glass preform lot according to any one of claims 1 to 3, and a glass preform taken out from the glass preform lot produced by the method according to claim 7 or 9. A method of manufacturing an optical element that heats the substrate and performs precision press molding using a press mold.   The method for producing an optical element according to claim 10, wherein the precision press molding using a glass preform press mold is performed by filling the glass in a sealed space formed with the press mold closed. .   The method for producing an optical element according to claim 11, wherein a precision press-molded product having a ridge composed of a free surface is formed.   The method for manufacturing an optical element according to claim 10, wherein at least two or more positioning reference surfaces are formed by precision press molding.

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